An
odyssey of discoverRoland Bunch describes the process
of discovery he and his colleagues went through over the last
two decades to identify 5 key principles of sustainable agriculture
for the humid tropics.

By Roland Bunch

Editor's Note

Ken Hargesheimer of the Mini-Farms Network sent
this Roland Bunch piece to us and said "You've
got to run this piece. Roland Bunch knows more
about no-till than anyone, having seen it in dozens
of countries."

Roland is renowned for his work promoting sustainable,
"people-centered" agriculture, through
World Neighbors in the 1980s, and now at COSECHA
(Associaiton of Consultants for a Sustainable,
Ecological and People-Centered Agriculture) in
Honduras. He is the author of Two Ears of
Corn: A guide to People-Centered Agricultural
Improvement, an influential book that has
been translated into several languages.

For more on COSECHA, click
here. For Roland Bunch's analysis of the successes
and failures of COSECHA's work in Honduras, click
here.

The odyssey of
my colleagues and I started in 1982, the day Conrado Zavala,
a Honduran villager, sheepishly showed us his experiment.
Skeptical about the value of the organic matter we had recommended,
he had piled a huge quantity of compost into several rows
of his maize field. The last two rows he left as a control
untilled and unfertilized. There, before our eyes, stood a
field of 2 1/2 m maize, with a last row less than 40 cm tall.
That was the day we began to realize the incredible degree
to which organic matter can restore soils.

1. Maximize
organic matter production

Little by little, work in a dozen countries has convinced
us that the vast majority of soils can be made highly fertile.
How? By using our first principle: maximize organic matter
production.

Conrado’s particular approach, however, was anti-economic.
The cost of using compost on basic grains exceeds the benefit.
But intercropped green manure/cover crops (gm/cc’s)
can produce from 50 to 140 T/Ha (green weight) of organic
matter with very little work: no transporting of material
and no cutting up or layering or turning over of compost heaps.
In fact, sometimes, because of the gm/cc’s control of
weeds, net labor costs decrease. And soil quality often improves
visibly each year.

Then, as often happens, we found we were far from the first
to employ intercropped gm/cc’s. Gradually, between 1985
and 1992, we learned that villager farmers from Veracruz State
in Mexico through Guatemala, El Salvador, and Honduras were
intercropping velvetbeans (Mucuna pruriens), cowpeas (Vigna
spp.) and jackbeans (Canavalia ensiformis) with their maize
and sorghum.

2. Keep
the soil covered

To our amazement, these systems, virtually all of them in
the supposedly infertile humid tropics, allow farmers to plant
maize every year for decades, with productivity increasing
over time up to 4 T/Ha. In other words, these farmers have
found an answer to slash-and-burn agriculture.

Migratory agriculture is most frequently motivated by decreasing
fertility, increased weed problems, or both. In the Mesoamerican
gm/cc systems, nitrogen fixation and biomass recycling maintain
soil fertility. Mulches of crop residues and fast-growing
gm/cc’s drastically reduce the weed problem. We had
learned a second principle: keep the soil covered.

Gm/cc mulches provide a whole series of additional benefits.
They protect the soil from irradiation and the heat of the
tropical sun, thereby also reducing burn out of organic matter.
They save a tremendous amount of work; farmers can sow into
the plant residue rather than tilling the soil. They keep
the excess nitrogen from acidifying the upper soil horizons.
And they largely prevent soil erosion, even on slopes of 40%.

In the meantime, we had been reading Fukuoka’s book,
The One-Straw Revolution. However, his recommendation of zero
tillage failed to convince us. After all, most of the traditional
agriculture in Latin America uses zero tillage, yet is far
from productive.

In mid-1993, I visited the work of EPAGRI in southern Brazil.
Having visited over 160 agricultural development programs
through the years, I found this largely unpublicized effort
to be the finest of its size I had seen in Latin America.
Literally tens of thousands of animal traction farmers were
producing harvests approaching those in the USA--with gm/cc’s
and zero tillage.

3. Zero
tillage

Valdemar de Freitas, EPAGRI’s manager, showed
us that the secret to achieving zero tillage is applying massive
amounts of organic matter to the soil. Brazilian farmers,
after some four years of applying gm/cc’s to the soil,
are able to quit ploughing. (This is now outdated, as corroborated
recently by Valdemar: "We now know that plowing down
green manure is a much, much slower way to improve soil structure
than going straight to zero tillage. The enhanced biological
activity under zero tillage is the key to soil structure renovation.")

The advantages of zero tillage, in terms of better soil structure,
reduced soil compaction, higher fertility, and decreased cost,
are impressive. Interestingly, farmers often use non-leguminous
gm/cc’s to increase biomass in order to quit ploughing
sooner. That is, they spend scarce income on chemical nitrogen
fertilizer for three or four years in order to achieve zero
tillage sooner.

The Brazilians’ discovery explains why the zero tillage
gm/cc systems of northern Honduras--and Fukuoka’s--produce
so well, while many traditional zero tillage systems do not.
Thus we added a third principle: use zero tillage.

4. Maintain
biological diversity

EPAGRI’s investigation and dissemination of over 60
species of gm/cc partly to avoid diseases and insect pests,
confirmed another, more widely known principle: maintain biological
diversity.

5. Feed
plants through the mulch

The last principle was discovered by Martha Rosemeyer,
a Cornell doctoral candidate working in Costa Rica. For several
years, agronomists working with a low-cost, traditional, mulched-bean
(Phaseolus vulgaris) system had been trying to solve a phosphorus
deficiency problem. With highly acid (pH = 4.0 to 4.5) soils,
virtually all the phosphorus applied became tied up almost
instantly. Farmers’ harvests averaged 500 kgs/Ha.

Martha and a group of farmers tried broadcasting the phosphorus
on top of the mulch. The results, since confirmed in numerous
additional experiments, were astounding. Bean yields rose
to between 1.5 and 2.5 T/Ha.

This phenomenon has not yet been validated with other crops.
Yet it would help explain the success of Mesoamerica’s
gm/cc systems, and coincides with the fact that plants as
diverse as maize, manioc, and tropical trees tend to develop
a heavy mass of feeder roots immediately under thick mulches.

Furthermore, it makes simple sense: when soils are as hostile
to plant growth as are the humid tropic’s acid soils,
feeding plants through a mulch would seem a much more promising
alternative. The fifth principle is undoubtedly the most unconventional:
feed plants through the mulch.

These five principles enjoy a nice synergy. For example, if
we are going to feed our plants through a mulch, we certainly
cannot plough our fields. Nevertheless, the most important
relation between these principles is precisely the one that
took us the longest to figure out: they describe quite well
the way a humid tropical forest functions. That is, all we
discovered in our 12-year odyssey is something we should have
guessed all along. In order for humid tropical agriculture
to be both highly productive and sustainable, it must imitate
the highly productive, millions-of-years-old humid tropical
forest.

Three months ago, I searched the computerized agricultural
data system in the United States for information on the nutrient
dynamics in mulches and the feeding of crops through a mulch.
I found virtually nothing. The above principles mean we are
going to have to develop agricultural systems totally different
from those agronomists have tried, for so many years, to "transfer"
from the temperate nations.

The possibilities are enormous. A study from northern Honduras
shows that the gm/cc/maize system there is 30% more profitable
than the high-input maize system nearby. It may well be we
are just beginning to fathom the full potential of low-input
agriculture in the humid tropics.